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Sure. You can see it in action at http://darklang.com/launch/demo-video http://darklang.com/launch/demo-video (also, we've gone through our waiting list, so we'

Sure. You can see it in action at http://darklang.com/launch/demo-video http://darklang.com/launch/demo-video (also, we've gone through our waiting list, so we're pretty much adding new folks who sign up immediately, if you want to try it out). The main idea is that you when you make a change (let's say, you type a key in the editor), that change happens directly on the AST (the internal set of objects that represent the program). So for example, if you're seeing: let x = 5 x + 2 we represent that internally as `Let ("x", Int 5, BinOp ("+", Var "x", Int 2))` In a normal programming environment, you type up text, and the parser converts it to the internal representation. With Dark, we always keep everything in the internal representation. That means, if it isn't a "syntactically" valid program, you can't create it in the first place. In practice, this means that if you type, for example, `z` in the middle of `let`, in a traditional language you'd get an error like `lzet is not a valid token` and in Dark, the `z` just wouldn't appear (nothing would happen). So it's not possible to get a syntactically invalid program. The overall idea with Dark is that programs are always live (and also safe). So to make that be true, we need to ensure that you don't spend a period of time in a state where we can't understand your program (such as when the syntax is invalid).

saagarjha 6y ago
That sounds…potentially confusing? Correct me if I'm wrong, but it just continues to run the last version of the program without errors, but it won't tell you if the current version is syntactically invalid?
- pbiggar 6y ago
  Think I made it more confusing, not less, sorry! Did you watch the video - it's clearer after watching it.
rgbrenner 6y ago
You have a grammar... you're just enforcing the rules when data is entered. The same as if my editor stopped accepting input if I miss typed a line until it was fixed.. or if I was required to select one of it's autocomplete suggestions. let x = 5 "hi " ++ name DB::set{} Are you saying these lines from the video are not consistent throughout? Like in one part I'll type "x = 5" to assign 5 to x, but somewhere else I'll have to type "5 # x" to do the same? Like just random syntax everywhere? If not, then you have a grammar. You should document it and treat it as such.
- pbiggar 6y ago
  I had to look up whether you were technically accurate (I've a PhD in compilers but parsing's not really my thing), and I think the answer is "it depends, maybe?" To get to the root of the issue though, there is not a parser. Well, one could consider the function that takes each keystroke to be a parser - though I don't know if that's technically correct either. So perhaps the more accurate thing to say is there is not a step that takes a textual source file and parses it.
  - GreedCtrl 6y ago
    What would happen if you paste a complete program in all at once?
    - pbiggar 6y ago
      That's not really how Dark works. You're not manipulating text in your editor - you use our editor, and our editor only uses ASTs. So when cutting and pasting, you're cutting and pasting AST, not text. So to answer your question, you can paste an entire handler or function at once, but it will be one you copied from another place in DArk and it will be structured. We've looked at allowing people to paste text (eg from Stackoverflow) into Dark. We think we can do it by just inserting each character one at a time (though there's a technical flaw with that at the moment, which could be addressed). In that sense, Dark is sort-of a parser (I don't know if it technically counts).
tomp 6y ago
So, looks like it's a textual language, it clearly has a syntax. How you manage the transition from text to AST and back, that's a different story - it might be that your approach is much better! (Though on the other hand it looks similar to how CLR/Roslyn C# compiler does it.)
- pbiggar 6y ago
  The code always lives as AST, and the code that you see in the editor is a pretty-print of the AST. We don't go back and forth between AST and text - when you make a change in the editor, we look up the "token" where your cursor was, and use it to find the place in the AST that needs a change, and changes only that.
WalterBright 6y ago
> That means, if it isn't a "syntactically" valid program, you can't create it in the first place. It's an interesting idea. I don't know if it would work for me, though. I don't write code as a stepwise refinement of a valid program, I massage the text gradually into a valid program. This is especially true when refactoring.
- pbiggar 6y ago
  Yeah, I think a bunch of people work like that. We've had the feedback that some people have had to change their workflow to work well with Dark. People generally use what we call "trace-driven development", where they make a HTTP request to the code they're editing (typically, people are making APIs or backends to JS apps), and then they always have "live values" of what they're working on (similar to a REPL, or to running unit tests on a loop, but instantly).

saagarjha 6y ago

That sounds…potentially confusing? Correct me if I'm wrong, but it just continues to run the last version of the program without errors, but it won't tell you if the current version is syntactically invalid?

pbiggar 6y ago
Think I made it more confusing, not less, sorry! Did you watch the video - it's clearer after watching it.

rgbrenner 6y ago

You have a grammar... you're just enforcing the rules when data is entered. The same as if my editor stopped accepting input if I miss typed a line until it was fixed.. or if I was required to select one of it's autocomplete suggestions. let x = 5 "hi " ++ name DB::set{} Are you saying these lines from the video are not consistent throughout? Like in one part I'll type "x = 5" to assign 5 to x, but somewhere else I'll have to type "5 # x" to do the same? Like just random syntax everywhere? If not, then you have a grammar. You should document it and treat it as such.

pbiggar 6y ago
I had to look up whether you were technically accurate (I've a PhD in compilers but parsing's not really my thing), and I think the answer is "it depends, maybe?" To get to the root of the issue though, there is not a parser. Well, one could consider the function that takes each keystroke to be a parser - though I don't know if that's technically correct either. So perhaps the more accurate thing to say is there is not a step that takes a textual source file and parses it.
- GreedCtrl 6y ago
  What would happen if you paste a complete program in all at once?
  - pbiggar 6y ago
    That's not really how Dark works. You're not manipulating text in your editor - you use our editor, and our editor only uses ASTs. So when cutting and pasting, you're cutting and pasting AST, not text. So to answer your question, you can paste an entire handler or function at once, but it will be one you copied from another place in DArk and it will be structured. We've looked at allowing people to paste text (eg from Stackoverflow) into Dark. We think we can do it by just inserting each character one at a time (though there's a technical flaw with that at the moment, which could be addressed). In that sense, Dark is sort-of a parser (I don't know if it technically counts).

tomp 6y ago

So, looks like it's a textual language, it clearly has a syntax. How you manage the transition from text to AST and back, that's a different story - it might be that your approach is much better! (Though on the other hand it looks similar to how CLR/Roslyn C# compiler does it.)

pbiggar 6y ago
The code always lives as AST, and the code that you see in the editor is a pretty-print of the AST. We don't go back and forth between AST and text - when you make a change in the editor, we look up the "token" where your cursor was, and use it to find the place in the AST that needs a change, and changes only that.

WalterBright 6y ago

> That means, if it isn't a "syntactically" valid program, you can't create it in the first place. It's an interesting idea. I don't know if it would work for me, though. I don't write code as a stepwise refinement of a valid program, I massage the text gradually into a valid program. This is especially true when refactoring.

pbiggar 6y ago
Yeah, I think a bunch of people work like that. We've had the feedback that some people have had to change their workflow to work well with Dark. People generally use what we call "trace-driven development", where they make a HTTP request to the code they're editing (typically, people are making APIs or backends to JS apps), and then they always have "live values" of what they're working on (similar to a REPL, or to running unit tests on a loop, but instantly).